In recent years, there have been problems with electromagnetic interference such as the malfunction of electronic equipment and the effect on a human body due to electromagnetic waves radiated from radio application equipment including a portable telephone. One of the measures against the electromagnetic interference is to dispose a conductive metal evaporated film on the inner surface of a resin body of a portable telephone for shielding purposes. The conductive metal evaporated film is effective as a shielding layer for preventing radiated electromagnetic noise from coming out of the portable telephone. In many cases, the conductive shielding layer is formed by a metal evaporation method, the application of a conductive coating, or the like. The conductive shielding layer needs to be connected electrically to a printed wiring board so that they are at the same potential. For this reason, a method has been employed in which spring metal contacts are fixed to an electrode on the printed wiring board, and the electrode is brought into contact with the conductive shielding layer to make an electric connection when the resin body is assembled (Patent Document 1).
Another method also has been proposed in which a metal foil or the like is integrated with one surface of conductive rubber, and then this conductive rubber is fixed on a printed wiring board using a conductive adhesive or other means to make an electric connection (Patent Documents 2 to 3).
The conductive rubber of such a component is produced by mixing insulating rubber and a large amount of conductive filler. Since the conductive rubber contains a large amount of conductive filler, the proportion of rubber in the entire volume is reduced. Thus, the rubber hardness becomes higher, and the initial compression load is increased. At the same time, the conductive rubber is likely to lose rubber elasticity or restoring force. Moreover, the conductive rubber significantly sacrifices the compression set properties, which are the important rubber properties. Consequently, the conductive rubber component is weakened and broken from the compression for a long period of time, and cannot be restored. Further, the resiliency of the conductive rubber is degraded, so that the electric connection to be maintained by the resiliency cannot be maintained in the end.
The conventional method generally includes integrating two materials with dearly different physical properties, i.e., a metal and an elastomer and cutting the resultant product to a desired size. However, when a sheet obtained by laminating the conductive rubber and the metal foil that differ in physical properties (e.g., rigidity and Young's modulus) is cut, burrs are likely to occur at the end of the product. This will be described with reference to the drawing. FIG. 9 is a cross-sectional view of a conventional laminate of conductive rubber and a metal foil. Conductive rubber 4 is laminated with a conductive adhesive layer 5, a primer layer 6, and a metal foil 7, and then integrated together. This laminate 11 is in the form of a sheet, and at least one end face is cut. Thus, a burr 8b occurs at the cut surface. As indicated by the arrow b in FIG. 9, the burr 8b is 80 μm or more in size and can increase the possibility of a defect that causes conductive anomaly, i.e., the product is mounted obliquely during reflow mounting.